EP1226708A1

EP1226708A1 - Signalling and transport of priority based control protocol messages over a switched communications network

Info

Publication number: EP1226708A1
Application number: EP00951102A
Authority: EP
Inventors: Ian Rytina; Leslie Gary Graf; Stephen Christopher Terrill; Christian Norman Groves; Mark Alan Hollis; Juan Noguera-Rodriguez
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 1999-08-13
Filing date: 2000-08-11
Publication date: 2002-07-31
Also published as: AUPQ220199A0; MXPA02001285A; EP1226708A4; WO2001013613A1

Abstract

The present invention relates to a method and apparatus for managing signaling of control protocol messages in a telecommunications node. More particularly, the invention relates to priority based signaling and transporting of control protocol messages in a telecommunications node. The present invention provides a method and apparatus for managing signaling in a telecommunications node, the node having separated BC and CC functionalities, the node also having control protocol messages for communication between the functionalities, including the steps of: allocating a priority value to a control protocol message, selectively processing the control protocol message based on the allocated priority value. Preferably, the allocated priority value is mapped to a priority mechanism of a signaling transport for transmission over a switched communications network.

Description

SIGNALLING AND TRANSPORT OF PRIORITY BASED CONTROL PROTOCOL

MESSAGES OVER A SWITCHED COMMUNICATIONS NETWORK FIELD OF THE INVENTION

The present invention relates to a method and apparatus for managing signalling of control protocol messages in a telecommunications node.

More particularly, the invention relates to priority based signalling and transporting of control protocol messages in a telecommunications node.

In one form, the present invention relates to a method of transmitting control protocol messages between a first entity and a second entity of a physically decomposed telecommunications node. The invention further relates to a method of transmitting media gateway control protocol messages on a prioritised basis between the first entity and the second entity. The present invention also relates to a physically decomposed telecommunications node including a first entity and a second entity and apparatus where priority based control protocol messages are transmitted between the first entity and the second entity. BACKGROUND OF INVENTION

For cost-efficiency reasons many telecommunications operators are increasingly deploying non-STM transport technologies, such as, for example, Asynchronous Transfer Mode (ATM), Internet protocol (IP) and Frame Relay (FR) inside their networks and therefore require a standardised solution to support existing services of today's public telecommunication networks over multi-vendor non-STM infrastructures. In the current public telecommunication networks, the call control (CC) and bearer control (BC) functions are tightly coupled in the same public network protocols, such as ISDN User Part (ISUP). As a result of this trend to run over multi-vendor non-STM infrastructures, a new network architecture has been developed that required the splitting of CC and BC into separate protocols. As a result of the splitting of the CC and BC, a new interface is exposed between the CC function and BC function. A protocol is required to enable the coupling between the CC and BC functions when a node is implemented in a separated environment. The International Telecommunications Union - Telecommunications Sector (ITU-T) Study Group 16 and the Internet Engineering Task Force (IETF) Megaco Working Group have developed one example of such a protocol, named a media gateway control protocol. This protocol is also known as H.248. The use of H.248 is not limited to multimedia networks such as, for example, networks complying with the H.323 standard of the ITU-T.

The media gateway control protocol is intended for use in networks where there is a physical decomposition of a traditional gateway function into two separate entities, namely a first entity called a Media Gateway Controller (MGC) and second entity namely a Media Gateway (MG). In the ITU-T Study Group 16 and in IETF Megaco Working Group the CC function is known as a MGC and the BC function is known as MG. Both the MGC and MG operate in a "client-server" relationship, where the MGC is seen as the server and controls the call logic of the physical connections in the MG. The MG is seen as the client, administering the actual physical connections of the media in response to commands sent from the MGC.

When reference is made to a physically decomposed telecommunications node this is equivalent to referring to a separated BC and CC telecommunications node. Examples of information passed from the MGC to the MG in H.248 protocol include information for ordering connection of one telephony circuit in the MG to another telephony circuit, that is when the MGC receives a request for a telephone call to be set up, information for ordering tones to be inserted into the MG's media stream and information for ordering disconnection of the circuits in the MG. Examples of information passed from the MG to the MGC in the media gateway control protocol are accounting information on the call duration, or statistical information on the current use of the media connections.

The type of information being carried in the H.248 signalling messages is varied and can be categorised into static data and dynamic data. Static data pertains to physical characteristics of a MG, for example passing information on the characteristics of a termination in a MG (which is a function of the AUDIT command), or the static data defines the functions that the MG has the capability of using.

Dynamic data on the other hand pertains to individual call connections such as the MG reporting observed call events in the MGC (for example NOTIFY command), or the MGC ordering the MG to modify terminations/contexts according to the state of the call, for example ADD, SUBTRACT, MODIFY commands. The AUDIT command can be also used by the MG to determine information on individual call connections, for example charging and statistics data pertaining to an individual termination. In a traditional telephony application, the amount of data passed between the MGC and MG is potentially very large and varied. In large scale applications, such as one for a local telephony exchange which could handle connections of tens of thousands of subscribers, it may be required to pass many thousands of messages per second on each MGC/MG H.248 signalling link. Signalling capacity therefore becomes an issue for telecommunications operators who are seeking to both maximise the call throughput, in order to increase revenue, and the signalling link usage, in order to minimise hardware costs. Where the signalling link is utilised on a "first come, first served" basis, the link characteristics may suffer in that for example, during a busy period, with many calls being handled by the MGC and MG it is important to the operator that the calls reach a chargeable state and are successfully executed. That is, the H.248 dynamic data messages are all completed quickly and successfully. If a large static data message is inserted onto the signalling link, it is highly likely that some of the dynamic data commands will fail due to signalling link overload. Calls will subsequently be dropped and call revenues and performance statistics of the system will decrease. SUMMARY OF INVENTION

It is an object of the present invention to overcome or ameliorate at least one of the problems of the prior art. Furthermore, it is desirable to provide a method and apparatus for transmitting control protocol messages between entities of a physically decomposed telecommunications node which ameliorates or overcomes one or more of the abovementioned disadvantages.

It would also be desirable to enable the transport of control protocol messages, such as media gateway control protocol messages, between entities of a physically decomposed telecommunications node, such as a media gateway controller and a media gateway of a physically decomposed gateway, without causing failure of various commands due to overload a particular signalling link.

In one aspect the present invention provides a method of managing signaling in a telecommunications node, the node having separated BC and CC functionalities, the node also having control protocol messages for communication between the functionalities, the method of managing signaling including the steps of: allocating a priority value to a control protocol message selectively processing the control protocol message based on the allocated priority value.

In another aspect the present invention provides a telecommunications node having separated BC and CC functionalities and having control protocol messages for communication between the functionalities, an apparatus for managing signaling between the functionalities including: priority allocating means for allocating a priority value to a control protocol message processing means for selectively processing the control protocol message based on the allocated priority value.

In essence, the present invention stems from the realisation that the capacity of a signalling link in a BC and CC separated telecommunications node can be increased by applying a priority mechanism in the media gateway control protocol.

According to a further aspect of the invention, there is provided a method of transmitting control protocol messages on a prioritised basis between a first entity and a second entity of a separated BC and CC telecommunications node, wherein media connections in said second entity being controlled by said first entity, the method including the steps of: creating a control protocol message in one of said entities; assigning to the control protocol message a priority value; transmitting said control protocol message over a switched communications network to the other one of said entities; and wherein said other one of said entities, on receipt of said control protocol message, selectively processes said control protocol message based on the assigned priority value.

The first entity may be a signalling and resource control gateway, such as a media gateway controller, and the second entity may be a media termination gateway, such as a media gateway. The control protocol message may be a media gateway control protocol message. The telecommunications node may be a physically decomposed media gateway.

The priority values may be assigned to commands, actions and transactions forming part of each message. The first entity or second entity may accept each priority value for each message as an input for sending the message and map the priority value to a signalling transport mechanism such as IP, ATM or MTP3 for transporting each message between the first and second entities.

The priority values may be assigned dynamically on a per-situation basis and/or a per-command basis. According to another aspect of the invention there is provided a separated

BC and CC telecommunication node including a first entity and a second entity, wherein media connections in said second entity are controlled by said first entity, said node including: means for creating a control protocol message and assigning a priority value to said control protocol message in one of said entities; means for transmitting said control protocol message over a switched communications network to the other one of the entities; wherein on receipt of said control protocol message, said other one of the entities selectively processes said control protocol message based on the assigned priority value.

In this way, the control protocol messages are transmitted over a switched communications network between entities of a physically decomposed telecommunications node on a prioritised basis, to substantially prevent failure of various commands where a signalling link is disrupted. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will hereinafter be described in a preferred embodiment, by way of example only with reference to the accompanying drawings wherein:

Figure 1 is a schematic representation of interfaces and functions of an H.323 gateway;

Figure 2 is a schematic representation of one embodiment of a physical decomposition of a telecommunications node, such as the H.323 gateway of figure 1 , where it is decomposed into a MGC and an MG;

Figure 3 is a graphical representation of various parts of a control protocol message, such as a media gateway control protocol message exchanged between the MGC and an MG of figure 2; and

Figure 4 is an example list of command messages transmitted between the MGC and MG having assigned thereto a priority value. DETAILED DESCRIPTION OF EMBODIMENTS

Although reference is made herein to gateway functions in accordance with

ITU-T recommendation H.323, this is by example only and the invention can equally be applied to physically decomposed gateway functions embodied in Bearer Independent Call Control, BICC, and Session Initiation Protocol, SIP, networks.

With reference to figure 1 , there is shown a representation of a group of interfaces and functions of a multimedia gateway 1 operating in accordance with ITU-T recommendation H.323. The multimedia gateway 1 is an end point on an H.323 multi media network that provides for. real-time two-way communications between terminals on the packet-based H.323 network and other ITU-T terminals on a switched circuit network communications network, such as ISDN or PSTN terminals, or to another H.323 gateway. Whilst the present invention will be described in relation to multimedia gateways, it is to be understood that it is equally applicable to terminals, gatekeepers, multi point controllers, multi point processors and other telecommunications nodes forming part of a multimedia network. The multimedia gateway 1 includes signalling termination points 2, 3 and 4 respectively acting to provide an interface between RAS signalling messages, H.245 signalling messages and H.225 signalling messages in an H.323 network and a gateway control logic unit 5. A further signalling termination point 6 acts to provide an interface between Facility Associated Signalling SCN messages and the gateway control unit 5. An SCN signalling transport termination point 7 provides an interface between the signalling termination point 6 and an SCN network. The control functions of the gateway 1 are split between high layer resource control functions in the gateway control logic unit 5 and lower layer resource control functions provided by a gateway device 8. A packet/circuit component 9 terminates SCN media channels that converts the media streams to packet based media on the packet network interface. The Y indicates the external packet interface and the Z indicates the external SCN interface.

The functionality of the media gateway 1 may be physically decomposed into a first entity, represented as a media gateway controller, and a second entity represented as a media gateway. Figure 2 shows one example of such a physically decomposed multimedia gateway 10. In this example, the FAS SCN services provided by the termination points 6 and 7 are isolated, together with the gateway device function, in a media gateway 12. The H.323 signalling is retained in a media gateway controller 14. In general, it can be said that the media gateway 12 acts to convert media provided from one type of network to the form required in another type of network. The MGC 14 controls those part of the call state that pertain to connection control for media channels in the media gateway 12. From figure 2 it can be seen that the physically decomposed multi media gateway 10 exposes a device control interface A between the gateway control logic unit 5 and the gateway device functions 8, as well as an SCN signalling interface C between the gateway control logic unit 5 and SCN termination functions 6 and 7. Messages are therefore required to be exchanged on the A and C interfaces between the MGC 14 and the MG 12 over an external telecommunications link. The media gateway control protocol or H.248 protocol defines a general framework for exchanging such messages between elements of a physically decomposed multi media gateway.

The media gateway control protocol describes resources in the BC function of MG 12 in terms of contexts and terminations. A termination represents a physical endpoint and can be assigned different characteristics, for example the transport type (circuit, IP, ATM) or media or codec type (GSM, G.711 ). A termination is in other words an entity that sources and/or sinks media streams. In the case of a multi media conference, a termination describes all media streams that originate from or are sent to the one user. A context, on the other hand, groups a number of terminations into a single conference, to describe a path or call through the BC function or a function internal to the BC function. Commands from the MGC 14 to the MG 12 are grouped into transactions, each of which is identified by a transaction ID. Transactions consist of one or more actions wherein an action consists of a series of commands that are limited to operating within a single context. Consequently, each action typically must specify a context ID. An example of a transaction 20 is shown in figure 3 where it consists of three particular actions 22, 24 and 26. Within each action there are a number of commands as shown.

The H.248 protocol provides Commands for manipulating the logical entities of the protocol connection model, Contexts and Terminations. Commands provide control at the finest level of granularity supported by the protocol. For example, Commands exist to add Terminations to a Context, modify Terminations, subtract Terminations from a Context, and audit properties of Contexts or Terminations. Commands provide for complete control of the properties of Contexts and Terminations. This includes specifying which events a Termination is to report and which signals/actions are to be applied to a Termination.

Examples of the commands used in H.248 include the Add command which adds a termination to a context. This command is generally used to create new terminations and add them to a context. This context may also be implicitly created when adding a termination to a new context. The Modify command modifies the properties of a termination and could also be used to change the properties of a context. The Subtract command disconnects a termination from its context and returns statistics on the termination's participation in the context. The Move command automatically moves a termination to another context and the Audit command returns the values of properties of the terminations and media gateway capabilities. The Audit command may also be used to query the properties of a context. Finally, the Notify command allows the MG to inform the MGC of the occurrence of events in the MG.

In figure 4 there is shown a table 30 specifying a number of example commands in the first column that are transmitted between the MGC and the MG. All commands except the Notify command and ServiceChange command are sent to the MG by the MGC. The Notify and ServiceChange commands are sent to the MGC from the MG. The Audit command may also be sent from the MG to the MGC. A priority mechanism in the H.248 protocol is applied to each specific command. Each message sent from the MGC or the MG would therefore be allocated a priority value according to its perceived importance in the MGC/MG system, as is specified in the second column in the table. The MGC, or MG depending on the command would take this priority setting as an input for sending a message and will map it to the appropriate signalling transport mechanism.

Assuming there is a wide variety of signalling transport mechanisms for H248, these priority values would be mapped by the MGC and MG into existing priority mechanisms in each transport and consequently transported accordingly. By way of example, for Internet Protocol (IP) transport of H.248 messages the priority values could be mapped by the MGC/MG to the IP "Type of Service" values. For Asynchronous Transfer Mode (ATM) transport, the priority values could be mapped into Virtual Circuit Identifier/Virtual Path Identifier (VCI/VPI) combinations. For the message transfer part (MTP), for example, in particular the level 3 (MTP3) transport mechanism, the priority values could be mapped to different Signalling Link Set (SLS) values. Examples of all these mappings are shown in the table of figure 4. Four different command priority values are assigned where priority 1 is the highest priority and priority 4 is the lowest priority. As an example, for IP, the ADD command has priority 1 and is mapped into the Type of Service field in the header in the category "immediate, minimise delay". For ATM it is mapped into the header portion of the packets under the VCI/VPI fields. In this particular example there are three different types of VCI/VPIs, being x, y and z, for carrying the H.248 messages. For the MTP3 there are two different types of priority being a, b and the ADD command is carried over the signalling link represented by SLS value a. For ATM the ADD command is carried over the VCI/VPI represented by the value x. For the IP header there are 32 different values in the IP Header Type of Service field. If each of the commands are combined together into actions, as shown in figure 3, a further mapping is required in the MGC/MG system and that is to provide the particular action with a priority based upon the priority of the commands contained within that action. For example, the action will have the same priority as the lowest priority of all of the commands contained within that action. Similarly, if these actions are combined into transactions, then a further mapping is required, for example the transaction may have the same priority as the lowest priority of all of the actions contained within the transaction.

The above examples of commands in figure 4 assume a static priority configuration. Alternatively, in particular situations a more dynamic priority configuration is required. For example, in severe congestion cases between the MGC and MG, it is not desirable to give higher priority to dynamic data commands, such as Add, Modify or Subtract since this would lead to worse congestion due to overload on the particular signalling link. Therefore in this situation it would be required that the priority is given to a static data command, such a ServiceChange so as to clear the congestion as quickly as possible. The ServiceChange command allows the MG to notify the MGC that a termination or a group of terminations is about to be taken out of service or has just been returned to service.

Thus, the MGC/MG could be given an option to set the priority dynamically on a per command, per situation basis. Thus each message is assigned a specified priority level, depending on the application that uses the media gateway control protocol or H.248 protocol. In particular the commands used are assigned with a particular priority level according to the situation at the time it is assigned. The media gateway control protocol would then map the priority it has received from its user to the priority setting associated with the particular transport mechanism used, whether it be, for example, IP, ATM or MTP3.

By assigning commands with a particular priority on a dynamic basis it prevents any low priority messages from distributing link characteristics. This will aid existing systems, based on STM, ATM or systems having similar mechanisms to smoothly adapt to new network architecture which allows one entity, being the MGC, to control media connections in another second entity, being the media gateway.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A method of managing signaling in a telecommunications node, the node having separated BC and CC functionalities, the node also having control protocol messages for communication between the functionalities, the method of managing signaling including the steps of: allocating a priority value to a control protocol message selectively processing the control protocol message based on the allocated priority value.

2. A method as claimed in claim 1 , wherein a priority value is allocated to each control protocol message.

3. A method as claimed in claim 1 or 2, further including the steps of: accepting the priority value as an input to a functionality for transmitting, and; mapping the priority value to a priority mechanism of a signaling transport.

4. A method as claimed in claim 1 , 2, or 3, further including the step of transmitting the control protocol message over a switched communications network.

5. A method as claimed in claim 3 or 4, wherein the signaling transport is IP, ATM or MTP3.

6. A method as claimed in any one of claims 1 to 5, wherein the control protocol message includes transactions.

7. A method as claimed in claim 6, wherein the transactions include actions.

8. A method as claimed in claim 7, wherein the actions include commands.

9. A method as claimed in claim 8, wherein priority values are allocated to the commands, actions or transactions.

10. A method as claimed in any one of the previous claims, wherein a priority value is allocated dynamically.

11. A method as claimed in claim 10, wherein a priority value is allocated on a per-situation basis.

12. A method as claimed in claim 10, wherein a priority value is allocated on a per-command basis.

13. A method of signaling within a telecommunications node, the node having separated BC and CC functionalities, the node also having control protocol messages for communication between the functionalities, the method of signaling including the steps of: managing the control signaling in accordance with the method of any one of claims 1 to 12, and transmitting the control protocol messages over a switched communications network.

14. A method of transmitting control protocol messages on a prioritised basis between a first entity and a second entity of a separated BC and CC telecommunications node, wherein media connections in said second entity being controlled by said first entity, the method including the steps of: creating a control protocol message in one of said entities; assigning to the control protocol message a priority value; transmitting said control protocol message over a switched communications network to the other one of said entities; and wherein said other one of said entities, on receipt of said control protocol message, selectively processes said control protocol message based on the assigned priority value.

15. In a telecommunications node having separated BC and CC functionalities and having control protocol messages for communication between the functionalities, an apparatus for managing signaling between the functionalities including: priority allocating means for allocating a priority value to a control protocol message processing means for selectively processing the control protocol message based on the allocated priority value.

16. Apparatus as claimed in claim 15, wherein the priority allocating means allocates a priority value to each control protocol message.

17. Apparatus as claimed in claim 15 or 16, wherein the node is a H.323 gateway.

18. Apparatus as claimed in claim 16 wherein the CC functionality resides in a Media Gateway Controller.

19. Apparatus as claimed in claim 17 or 18 wherein the BC functionality resides in a Media Gateway.

20. Apparatus as claimed in claim 17, 18 or 19 wherein the control protocol message is a Media Gateway control protocol message.

21. Apparatus as claimed in claim 20 wherein the control protocol message includes transactions.

22. Apparatus as claimed in claim 21 wherein the transactions include actions.

23. Apparatus as claimed in claim 22 wherein the actions include commands.

24. Apparatus as claimed in claim 23 wherein the priority allocating means allocates priority values to the commands, actions or transactions.

25. Apparatus as claimed in any of claims 15 to 24 wherein the priority allocating means includes dynamic allocating means for dynamically allocating a priority value.

26. Apparatus as claimed in claim 25 wherein a priority value is allocated on a per-situation basis.

27. Apparatus as claimed in claim 25 wherein a priority value is allocated on a per-command basis.

28 In a telecommunications node having separated BC and CC functionalities and having control protocol messages for communication between the functionalities, an apparatus for signaling between the functionalities including: an apparatus for managing signaling between the functionalities as claimed in any one of claims 15 to 27.

29. A telecommunications network including an apparatus as claimed in any one of claims 15 to 28.

30. A telecommunications system including an apparatus as claimed in any one of claims 15 to 28.

31. A method as herein disclosed.

32. A network, system, protocol or apparatus as herein disclosed.

33. A separated BC and CC telecommunication node including a first entity and a second entity, wherein media connections in said second entity are controlled by said first entity, said node including: means for creating a control protocol message and assigning a priority value to said control protocol message in one of said entities; means for transmitting said control protocol message over a switched communications network to the other one of the entities; wherein on receipt of said control protocol message, said other one of the entities selectively processes said control protocol message based on the assigned priority value.